I am helping my daughter with a science fair project about vegetation and runoff. She has four trays of different soil types she collected from One area in a vacant lot behind our house. One tray is just soil(with rocks), one tray just grass and soil, one tray with soil and vegetation growing on top, and the fourth tray with soil and organic matter(leaves,clippings,etc.). She wants to set tray at angle and water with a sprinker (on spray setting) so that each plant will be watered evenly. The runoff will run out of tray and be caught underneath. The water that soaks into soil will be caught directly underneath the pot. She wants to see the runoff versus what percolates through ground. She then asked if she could fertilize the trays before watering, and then test each of the runoff trays for different pollutions (phosphorus, nitrates, etc.) Does this seem like it will work? She is trying to show how runoff water is potentially dangerous.

This is a really great project, and your daughter's idea makes it very relevant to what is happening with farming. My only advice would be to make sure that she adds the same amount of the same kind of fertilizer to each treatment. She needs to control as many variables as possible, so she should make sure to add the fertilizer in the same way and for the same amount of time prior to watering. Otherwise, the experimental design sounds good!

Please post again (in this same thread) if you have any more questions, and I would love to hear how everything turns out!

Two last questions. She wanted to fertilize with granule fertilizer. I was just wondering if liquid fertilizer that is mixed with water would be better since it would seep into soil faster. Does that make a difference?

Second, she has to do five trials. How many times should she water and test to make one trial? Would it be just watering once and testing as on trial or several waterings? She thought one since it it as if it was the runoff process on one rain.

Great questions! It is possible that you would see a difference between the runoff coming from granule fertilizer and that from liquid fertilizer. If you have enough trays, your daughter could test the difference by doing the same four treatments (soil alone, grass, vegetation, and leaf litter) with each fertilizer.

The number of waterings per trial is up to your daughter. Once is perfectly fine. To do independent trials, she would need to set up brand new trays for the other trials. Alternatively, she could have 5 of each type of tray, and run the experiment once. Does that make sense?

Yes, that made sense. We tried a trial with all four soil samples and she couldn't get any nitrate reading with the strips. She used a 14x11 Kitty litter pan(15 cups of soil) and used 1 tsp granule fertilizer. Should we use more? I was afraid if we used more it would cause all of the readings to be the same or does that matter ?

Also, she put 15 cups of soil in each pan. Then we added the vegetation to one pan, organic to another and grass to one. Is that ok? I didn't know a way to keep it constant in the make-up of the pans, i.e. the vegetation to soil ratio, organic matter to soil ratio, etc. Does it matter on the amount of each item placed in the pan? Just wondering!

Again, you have very good questions! For the fertilizer, 1 tsp does seem like a small amount for 15 cups of soil. Are there instructions on the fertilizer that advise a certain amount for a given amount of soil? A bit of online research might help you there. Even if you don't find recommended amounts, it makes sense to increase the amount of fertilizer because you need to get a reading, and the larger question is how much the vegetation helps prevent the erosion and thus the leaching of nitrogen.

To answer your second question, it does matter how much organic matter you add to the pan. I think your best bet is to be consistent, and measure a common volume (or weight) of each type. It is especially important to keep things the same within treatments (i.e., always use the same amount of grass), but it is also important to try to control variables between treatments, so it's not the amount of matter but the type that will drive any differences you observe.

Keep at it, and please let me know if more questions come up along the way.

I am not sure where my brain was when I helped my daughter figure out the measurements. Yes, it is way more than 1 tsp...more like 5tsp.

We ran another trial and the vegetation had a great amount of runoff compared to the other pans. I am assuming that maybe we are having a problem with even watering from the sprinklers.. We tried to make sure that only runoff water got into the run off pans and that when we watered the soil pan no extra water flying from the sprinkler got in. Just wondering if we could do the same experiment with a watering can and a use the same amount of water to water each pot instead of the sprinklers? Or do you think we should continue to try to get the sprinklers to work? I am willing to keep looking for a solution if you think the sprinklers make this more "scientific".

I love your enthusiasm and your perseverance! I think a watering can is perfectly scientific, because you as the scientist are better able to control the amount and direction of the water falling on the treatments.

That said, it sounds like you already got some results. It's okay if they were different from what you and your daughter expected.